Features of Liquid Crystal Display Materials and Processes Part 9 potx

Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays Property Resolution Panel Diagonal Speed contrast 149 Specification 1024 x 768 6.0 inch diagonal 240Hz 1000：1 Table Image Liquid Crystal panel specification 3.3.1 Experimental results The photographs of displayed images used the luminance meter (Konica Minolta CS-200) as shown in Fig 20 The distance from the optical sensor to the center of LED backlight panel is in 60 cm, which is the normal range of distance for watching a 3D computer monitor Measurements of angle are done from observation point -50 degree to observation point +50 degree; view is the central view The illuminance meter has an analog output to the oscilloscope and the illuminance signal can be recorded and processed by a computer Fig 20 Four views backlight In this research, we observed backlight light stain structure for 3D image display based on lenticular lens array In Fig.21, the photo is illustrated for four viewing zones 1-4 located at the viewing location Each viewing zone uses 1/240 second to display one image The light source at specific location is grouped corresponding to each lenticular lens of the lenticular lens array For the four viewing zones, each lenticular lens has four groups 1-4 of light sources corresponding to four viewing zones 1-4 The four groups of light are sequentially turned on for 1/240 second The group of light source is turned on, and then the group of light source is turned on next for 1/240 second Likewise, the groups and of light source are sequentially turned on for 1/240 second Generally, the multiple viewing zones equally shares 1/60 second for one image frame The viewable zone area from first viewing zone to be contiguous to second viewing zone is 90 mm, and for viewing zone of viewable area is 360 mm(The separation of viewing zones is about 90 mm, and overall width of viewing group is 360 mm) as shown in Fig 20 150 Features of Liquid Crystal Display Materials and Processes Yellow stripe pattern is created by phosphor of yellow color White LEDs are blue LED chips covered with a phosphor that absorbs some of the blue light and fluoresces with a broad spectral output ranging from mid-green to mid-red So, the backlight modular was taken on yellow stripe The configuration of uni-direction diffusion lens plate is shown in Fig 21(b) The panel of 240Hz displays the corresponding images of the four viewing zones by the same time sequence according to temporal multiplexed mechanism The uni-direction diffusion lens plate can condense the light individually belonging to each the lenticular lens at transverse direction The lenticular lenses of the lens array receive the light and deflect the light into each viewing zone in a time sequence, respectively Light intensity 7000 6000 A nits 5000 V1 4000 V2 3000 V3 2000 V4 1000 -50 -40 -30 -20 -10 10 deg 20 30 40 50 (a) Lenticular/LED Light intensity(Polarizer+uR+Polarizer+Len) 7000 V1 V2 V3 6000 V4 5000 FV(2/25) nits 4000 3000 2000 1000 -50 -40 -30 -20 -10 10 20 30 40 50 deg (b) Lenticular/Optical film/LED Fig 21 The crosstalk under different observation scanning angles According to the time sequence for turning the groups of the light source, multiple viewing zones at multiple directions are created To meet the requirements of different one-eye images, we propose that the real-time active barrier dynamic backlight slit system on stereodisplay The center viewing group has the least crosstalk, and side lobe groups have larger crosstalk, especially when viewing groups departs from center very much The crosstalk under different observation scanning angles is showed from data in Fig 21, including the cases of 4-views field scanning The crosstalk of view is about 5% respectively, the results are better than slanted lenticuler lens type Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 151 3.4 Multi-viewer tracking stereoscopic display This study integrated an autostereoscopic display with a viewer-tracking system Fig 22 illustrates the basic structure of the display and table shows the specifications of the image liquid crystal panel In the proposed structure, a retarder inserted between the image panels rotated the light beam at 90°; simultaneously, a lenticular plate adjusted the light direction to show the light slit from the tracking display Retarder film is a clear birefringent material that alters the phase of a polarized beam of light A quarter wave plate can convert linearly polarized light (oriented at 45° from the direction of the fast/slow axis) into circularly polarized light Conversely, the wave plate can convert a circularly polarized beam into linearly polarized light Fig 22 The structure of the proposed viewer-tracking display panel Property Resolution Panel Diagonal Speed contrast Response time (G2G) Specification 1920 x 1080 23.6 inch diagonal 120Hz 1000：1 2ms (3D) Table Image Liquid Crystal panel specification In this study, when the polarization direction of the incident light formed an included 45° angle with the optical axis of the retarder, the polarization of the light passing through the /2 retardation regions rotated by 90° and became orthogonal to the polarization of the light passing though the 0° retardation regions The molding method fabricated the lenticular plate with polymeric film as the substrate material One of the light slit pattern pairs adjusted the direction of light from the tracking panel to the viewer’s eyes through the lenticular plate In this display, the PDLC panel played an important role in the function of the 2D/3D switch When the PDLC panel was turned to clear state, the microretarder interacted with the polarizers to form a parallax barrier pattern as shown in Fig.23, making the display autostereoscopic In a case where the PDLC panel is in a diffusive state, the light passing 152 Features of Liquid Crystal Display Materials and Processes Fig 23 The pattern of a microretarder through the PDLC destroys the polarization The microretarder then loses its function as a parallax barrier, and the display becomes a general 2D display This study developed autostereoscopic display apparatus and a display method The autostereoscopic display apparatus included a display panel, a backlight module, a tracking slit panel and an optical lens array In a frame time, the display panel and tracking panel share the same synchronization signal for the display panel The tracking panel controls the light of the backlight module The tracking panel features tracking slit patterns and switches the slit patterns according to the synchronization signal Until all screen data is updated, the backlight module is inactive during the frame time A light provided by the part of the backlight regions passes through the tracking slit set, optical lens array, and the display panel in such a way that each eye separately perceives images As shown in Fig 24, when the viewer moves to the left, the tracking slit set changes its pattern to display the correct image Fig 24 Relations between viewer and tracking panel Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 153 The autostereoscopic display integrated a webcam as the real-time detection device for tracking of the viewer’s head/eye positions, so that the display showed left and right eye images correctly The computer vision-based tracking method detects viewer’s eyes over a specific range and under conditions of low and fluctuating illumination By capturing the image of the viewer in front of the display, the viewer’s position is calculated and the related position data is transferred to the field programmable gate array (FPGA) controller through RS232 When the viewer recognizes that he/she is standing at the borders of the viewing zones, analyzing the captured viewer images determines the border positions of the viewing zones The resulting eye reference pattern allows the tracker to locate the viewer’s eyes in live video images If an observer moves away from his original position, the tracking slit will vary its pattern according to the viewer’s new position The viewer still perceives two eye images separately before exceeding the webcam detection range Fig 25 shows the viewer-tracking system Fig 25 Viewer-tracking 3D display system This research addresses the specific technological challenges of autostereoscopic 3D displays and presents a novel system that integrates a real-time viewer-tracking system with an autostereoscopic display Our successfully designed prototype utilized a FPGA system to synchronize between a display panel and tracking slit panel With 120Hz display and tracking panels, only a pair of page-flipped left and right eye images was necessary to produce a multi-view effect Furthermore, full resolution was maintained for the images of each eye The loading of the transmission bandwidth was controllable, and the binocular parallax and motion parallax is as good as the usually lower resolution multi-view autostereo display 154 Features of Liquid Crystal Display Materials and Processes (B) LED Backlight architecture Many types of LED backlights are applied to 2D or 3D displays To date, research on 3D display systems has generally focused on providing uniform, collimated illumination of the LCD, rather than addressing low crosstalk issues This study investigated the method of using an autostereoscopic multi-viewer tracking 3D display with a synchro-signal LED scanning backlight module to reduce the crosstalk of right eye and left eye images, enhancing data transfer bandwidth while maintaining image resolution Fig 26A is a schematic view of a stereoscopic display Fig 26B is a block diagram illustrating the stereoscopic display; the stereoscopic display can track the viewer’s position and be watched by multiple viewers Stereo image display card Image Sync 120Hz Display panel R(1) R(2) Page-flipping R(3) R(4) OL OR Dynamic BLU 120Hz Tracking panel Fig 26A The schematic view illustrating a stereoscopic display Web cam viewer’s head position (Information) Ds Tracking pattern generation (slit data banks) viewer’s head Dv Choose pattern Stereo image display card Control Unit Sync Tracking pattern Dynamic Backlight Unit Tracking panel Display panel Fig 26B The block diagram illustrating the stereoscopic display Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 155 The backlight module of the stereoscopic display is a dynamic backlight module featuring many light-emitting regions R(1)~R(4) Fig 26A excludes the control unit and optical lens array In the stereoscopic display, the graphic card outputs and transmits the vertical synchro-signal to the control unit After receiving the synchro-signal, the control unit outputs the synchro-signal to control (turn on or off) the light-emitting regions R(1)~R(4) To meet the requirements of different one-eye images, we propose that the dynamic LED backlight tracking panel has have many backlight slit sets According to the position information of viewer O and the vertical synchro-signal, one of the slit sets of the tracking panels is selected and turned-on Each slit set includes either left or right eye slits Light emitted from the dynamic backlight module passes through the either left or right eye slit and the display panel, and projects onto one eye of viewer O Similarly, light emitted from the dynamic backlight module passes through the either left or right eye slit and the display panel, and projects onto the other eye of viewer O In this way, the pair images are projected to the two eyes of viewer O, who can see accurate three-dimensional images For example, light emitted from the dynamic backlight module passes through the left eye slit of the slit set and the display panel, and projects onto the left eye OL of viewer O Similarly, light emitted from the dynamic backlight module passes through the right eye slit of the slit set and the display panel, and projects onto the right eye OR of viewer O The one-eye slits are stripe-shaped and the lengths of the one-eye slits are approximately equal to the longitudinal length of the display panel When the display panel displays an image based on the vertical synchro-signal, the slit set of the tracking panel is enabled Meanwhile, pixels in the updated region of the display panel display a left-eye image, but pixels in the non-updated region of the display panel still display the previous right-eye image Light passing through the slit set of the tracking panel and the non-updated region of the display panel can be projected onto left eye OL of viewer O (i.e a crosstalk phenomenon) if no alternative methodology is applied This research proposes using a dynamic backlight module to suppress the crosstalk The light-emitting regions R1~R4 of the dynamic backlight module are separately controlled according to the vertical synchro-signal During a frame period, the light-emitting regions R(1) and R(2) corresponding to the updated region are turned on and the light-emitting regions R(3) and (4) corresponding to the non-updated region are turned off In this way, only the light-emitting regions R(1) and R(2) provide light, so that no light passes through the slit set of the tracking panel and the non-updated region of the display panel This reduces the crosstalk phenomenon of the stereoscopic display system As shown in Fig 26A and Fig 26B, the display method of the stereoscopic display comprises the following steps: First, slit data banks (Ds) corresponding to the many viewing angles of the stereoscopic display apparatus is established Next, the control unit receives information (Dv) on the position of the viewer The control unit compares the position information and the slit data banks stored in advance Meanwhile, the control unit outputs the vertical synchro-signal from the graphic card to control the output mode of the dynamic backlight module and operation mode of the tracking panel The display panel is driven to display images (i.e image updating) according to the vertical synchro-signal output from the graphics card Many of the light-emitting regions (R(1)~R(4)) of the dynamic backlight module are stripeshaped and the light-emitting regions R(1)~R(4) extend across the slits of the tracking panel The extending direction of the light-emitting regions R(1)~R(4) is perpendicular to the 156 Features of Liquid Crystal Display Materials and Processes extending direction of the slits of the tracking panel Many of the light-emitting regions (R(1)~R(4)) of the dynamic backlight module are array in an arrayed manner 3.4.1 Crosstalk analysis To avoid ghost images, the backlight modular provides backlight control signals which are dependent on the position of an associated part of the panel The system is provided for controlling synchronization timing between backlighting and pixel refresh, in dependence of a location of a section within the display panel The backlight unit is separated into several regions Let’s take regions as the example, the pixel response time is less than three fourths of the frame time when the illumination period is one quarter of the frame time Optical sensor and CS-100 Spot Chroma Meter of luminance crosstalk measurement of the 4regions 、2-regions scanning and strobe backlight method without lenticular Frame sequential(page flip, temporal multiplexed) process, the process is referred to as alternate frame sequencing Crosstalk is a critical factor determining the image quality of stereoscopic displays Also known as ghosting or leakage, high levels of crosstalk can make stereoscopic images hard to fuse and lack fidelity Crosstalk is measured by displaying full-black and full-white in lightemitting regions R(1)~R(4) of the display system without lenticular and using an optical sensor to measure the amount of leakage between channels For example, the optical sensor is placed at the left eye position (either behind the left eye of 3D glasses, or in the left eye viewing zone for an autostereoscopic display) and measurements are taken for the four cross-combinations of full-white and full-black in the left and right eye-channels An additional reading is also taken with the display in the off state These readings can then be used in the crosstalk equations described above This metric can be called black-and-white crosstalk and this metric is often used because maximum crosstalk occurs when the pixels in one eye-channel are full-black and the same pixels in the opposite eye-channel are full-white According to the results, the brightness of the 4R scanning backlight and the widened backlight strobe is about half of the 2R scanning backlight But the crosstalk performance of the widened backlight strobe crosstalk is the best of three methods Only about 1.68% left Although the 4R scanning backlight display crosstalk is higher than widened backlight strobe, it still performs better than the 2R scanning backlight one In the study, the CS-100 Spot Chroma Meter was used to measure the brightness of the backlights, which can be controlled using the duty cycle of backlight signal, as shown in Fig 27 Moreover, photodiode s3072 was used to measure the optic characteristics of the display device To view the correct image from the tracking display, the synchronization relationship between image display and backlight requires calibration Fig 28 shows that the V-sync signal exceeds the backlight signal in 1/160s If the V-sync signal triggers the backlight signal directly, the observer sees three white regions and one black region (not fully white or fully black) As the human eyes determine light source, a vertical signal must trigger the first region backlight (the dotted line of Fig 28) Fig 29 is the crosstalk of right eye and left eye under three different brightness conditions The phase of the V-sync signal exceeds the phase of the backlight signal in 1/480s It is too dark if the duty cycle is lower than 50%, so the three chosen duty cycles all exceeded 50% According to Fig.29, the differences in brightness not significantly affect the crosstalk The performances of both eyes were approximately in agreement The experiment selected maximum brightness Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 157 Fig 27 Optical sensor and CS-100 Spot Chroma Meter of luminance crosstalk measurement of the 4-regions , 2-regions scanning and strobe backlight method without lenticular Fig 28 The synchronization relationship between image display and backlight (from top to bottom) Fig 29 The crosstalk under different brightness conditions 158 Features of Liquid Crystal Display Materials and Processes Fig 30 shows the crosstalk of the right eye and left eye with different phase shifts between the V-sync signal and backlight signal, where the duty cycle of backlight signal is 100% The lowest crosstalk only occurs when phase shifts are 1/160s, not both 1/480s and 1/160s Here, light leaking to other regions and the response time of the liquid crystal affect the crosstalk (Fig.31) Fig 31 is the response reaction of the liquid crystal from full black to full white The horizontal axis is time (5 ms per grid) and the vertical axis is voltage (20 mV per grid) One display frame is 1/120 second, approximately equal to milliseconds The response waveform can be divided into four sections (2ms per section) The waveform of the liquid crystal still rises (section II) when the phase of V-sync signal exceeds the backlight signal in 1/480s (≒2ms); here, the phase does not reach a bright state But, the phase shifts of 1/240s (≒4ms) and 1/160s (≒6ms), located at region III and region IV, respectively, gradually near the bright state; this explains the difference in crosstalk Fig 30 The crosstalk under different phase shift conditions Fig 31 The response time of liquid crystal from dark state to bright state 3.4.2 Measured results (A) The optical properties measurement Detailed and quantitative measurements were used in the autostereoscopic display To measure the borders and the performance of the viewing zones, a luminance meter, Minolta CS-200, was located at the designed viewing distance (630mm from the display), which reduced the display panel’s optical interference during measurement Only the backlight module, including a backlight, tracking panel, and lenticular plate, was used in optical Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 159 luminance measurement experiments In this backlight structure, no additional brightness was lost in the optical path Fig 32 shows the results of the luminance intensity experiment The entire measuring process was completed in a darkroom, which provided measurements of fairly high quality In the luminance intensity experiment, only 40 degrees on both sides of the center of the backlight module was measured; the intensity value was captured every 0.5 degree When measuring, only one viewing zone of the tracking panel was switched on The luminance meter was used to scan the viewing zones horizontally The maximum peak luminance value of the viewing zone was approximately 514 cd/m^2 when CS-200 detected the luminance intensity value near the center of the backlight module The minimum peak luminance intensity value of the backlight was approximately 364 cd/m^2 at the edge of the viewing group The luminance intensity range of the viewing group in front of the backlight module ranged between 264 and 514 cd/m^2 The intersection point between two adjacent luminance intensity curves may determine the borders of the viewing zones Fig 32 Luminance intensity distribution of lenticular-type BLU After luminance intensity measurement of viewing zones to was completed, data could be combined to yield a luminance intensity distribution figure to verify the optical design parameters The peak luminance intensity value of viewing zone is in front of the center of the backlight module The tracking panel was slightly misaligned with the lenticular plate Due to the light intensity distribution of the tracking panel and the entrance angle difference of the light path between the backlight and the lenticular lens, a stronger luminance intensity curve was measured in the central part of the viewing group The viewing group of the 3D display system was approximately 53 cm wide at a viewing distance of 63 cm, indicating that each viewing zone is 6.625 cm wide on average In building a viewer-tracking-based autostereoscopic display, the viewer’s position and border positions of the viewing zones are the key parameters To accurately define the viewer’s position, the black and white pictures for both eyes were displayed as calibration images The positions of the borders in the viewing zones could be determined by analyzing the images of the viewer captured while the viewer reported to be at the border positions (B) Motion parallax function result For a 3D display to simulate the natural vision of human beings, both binocular parallax and motion parallax are required For a multi-view autostereoscopic display system, viewers can 160 Features of Liquid Crystal Display Materials and Processes see stereoscopic images with binocular parallax and motion parallax within a group of viewing zones However, a high number of viewing zones is necessary to achieve smooth motion parallax for a sufficiently large view This normally causes significant reduction of image resolution While maintaining good image resolution, we implemented smooth motion parallax by adopting viewer tracking function and real-time image updating in a two-view autostereoscopic display system (a) 35∘image content, (b) 40∘image content, (c) 45∘image content, (d) 50∘image content, (e) 55∘image content, (f) 60∘image content, (g) 65∘image content, (h) 70∘image content Fig 33 The viewer-tracking-based 2D/3D switchable autostereoscopic display This study used an ad-boost algorithm capable of evaluating important features to quickly track viewers If the viewer’s eyes were detected in specific viewing zones in front of the display, the viewer’s position would determine the images of the corresponding viewing angles shown When the viewer’s eyes move inside the same viewing zones, full stop needs moving, the images for the new viewing angles are fed into the same viewing zones The viewer experiences the motion parallax because he/she sees different images from different angle When the viewer’s eyes continue to move and finally cross the border of the viewing zones, the images of the new angle are reversed left-and-right and presented in real-time on the display In this study, tracking stability was good with viewing angles ranging from -15 degrees and 15 degrees The refresh rate achieved 30 frames per second when the resolution of the capturing image was set to 160×120 To match the resolution of the display, the resolution of image content for each eye was 840×1050 The image content was rendered from the 3D model built from 3D Max or directly captured using cameras For the webcam coordinates, the accuracy of one pixel was about 6.25 mm according to the viewing angle of the webcam indicated and the designed viewing distance in the autostereoscopic display Therefore, the rendering or capturing angle was set to 0.5 degree according to the accuracy of one pixel As shown in Fig 33, the 2D/3D switchable auto- stereoscopic display correspondingly Intelligent and Green Energy LED Backlighting Techniques of Stereo Liquid Crystal Displays 161 provides about 160 pairs of stereo images to the viewer moving in the viewing angle of the system The viewer is consistently able to experience the reality of motion parallax Conclusion The design of the three dimensional hierarchy with control circuit for large LED backlight array, which effectively reduces the terminal numbers into the cubic root of the total control unit numbers and prevent a block defect of the flat panel The display panel is divided into many scanning block parts, each part is separately and simultaneously scanned in the same directions to write images on the pixels on the respective scanning electrodes These defects are generally the result of a failure in the row (horizontal) or column (vertical) drivers or their connections We have reached the advantages of high accuracy, rapid selection, and reasonable switching speed flat panel Several shutter-glasses type stereoscopic displays have been measured to analysis difference of their 3D performance The less the backlight regions are, the brighter the display with scanning backlight method is Therefore, a 2R scanning backlight is brighter than a 4R one Nevertheless, due to better separation of a 4R scanning backlight, the crosstalk of it is less than that of a 2R scanning backlight However, from the other aspect, the uniformity of a scanning backlight method is usually not as good as than backlight strobe method For a higher luminance and lower crosstalk, it is suggested to combine the 4R scanning backlight method and backlight strobe method In this way, a 120Hz LCD can be made a very good performance stereoscopic display with shutter glasses In full resolution multi-view autostereoscopic display research, we have successfully designed and fabricated the optical system, high density active barrier dynamic LED backlight, the slit pitch is 700um, and the LED chip size is 10×23mil for full resolution multiview autostereoscopic display From the measurement results, the dynamic LED backlight optical system can yield ideal parabolic curvature and the crosstalk is lower than 5% Besides, the lenticular lenses of the lens array optical system was successfully received the light and deflected the light into each viewing zone in a time sequence, which could be one of the candidates for future full resolution time-multiplexed 3D applications A 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Health and Environmental Engineering, National Kaohsiung First University of Science & Technology, Kaohsiung 1USA 2Taiwan 2Department Introduction The fabrication of TFT-LCD panel includes the growing and etching of a-silicon and silicon nitride films These fabrication processes utilize significant amounts of silane, phosphine, ammonia, chlorine, boron trichloride, nitrogen trifluoride, fluorine, and hydrogen which are highly flammable, reactive, corrosive, and/or toxic The amount used and scale of the supply system for these gases are far larger than for other tech industries such as the semiconductor and photovoltaic industries Accidental leaks and fires of these gases are the major safety concern in the TFT-LCD fabs This paper first reviews the hazardous properties of the gases used in the TFT-LCD manufacturing processes The best practices for handling these hazardous gases are then described Finally, the past incidents and emergency response actions are also reviewed Hazardous properties of specialty gases The TFT-LCD manufacturing processes utilize significant amount of gases for thin-film deposition and etching These include silane, phosphine, ammonia, and hydrogen for polycrystalline silicon and silicon nitride thin film deposition in a plasma-enhanced chemical vapor deposition (PECVD) reaction chamber In addition, nitrogen trifluoride or fluorine is used in the PECVD chamber cleaning Chlorine and sulfur hexafluoride are used in the dry etching of thin film The hazards of these gases can be classified as pyrophoric, flammable and oxidizing gases There are other bulk gases such as nitrogen, argon and helium which are used for inerting or purging and will not be discussed here owing to their low risks 2.1 Silane Silane or silicon tetrahydride (SiH4) is the most common silicon source used in TFT-LCD manufacturing It is a highly flammable gas and has a very wide flammable range, from 1.37% to 96% Silane is colorless and odorless although it has been reported to have a prudent odor and a reported time weighted threshold limit value (TLV-TWA) of ppm by ACGIH However, this data is based on analogy of another hydride gas Germane rather than the actual toxicological data In fact, silane has no odor and its toxicity is low with a high median lethal concentration (LC50) of 9,600 ppm for rat at hours exposure The prudent odor comes from the impurity of trichlorsilane during early silane production 166 Features of Liquid Crystal Display Materials and Processes Silane is used as a compressed gas However, silane has a critical temperature of -3.4°C It is possible that liquefaction may occur in cold storage or during expansion cooling from compressed sources A silane supply system must be designed properly to prevent unexpected pressure surge from liquefaction and vaporization Silane is also a pyrophoric gas that normally ignites upon contact with air Silane has a reported autoignition temperature of -50~-100°C Autoignition of silane in air has also been reported down to -162°C, depending on the oxygen concentration of the mixture (Baratov et al., 1969) However, the autoignition temperature only denotes the temperature above which a given fuel-air mixture will autoignite in a closed vessel It however does not refer to details of the autoignition process and how autoignition is affected by flow The major potential hazard of silane is however not in its pyrophoricity but rather in its unpredictable ignition behavior in accidental releases A silane release from a pressure source has been known not to lead to spontaneously ignition (Koda, 1992) and frequently delayed ignition occurs when the release is shut-off resulting in a “pop” In a semi-confined space with gas accumulation, the pop can lead to a gas explosion with significant damage (Ngai et al., 2007) The mechanism of delayed ignition has been studied by Tsai et al (2011) which demonstrated that silane release without prompt ignition was most likely caused by quench of the reactive kernel from the flow strain or scalar dissipation accompanied by the large velocity and concentration difference between the release gas and the ambient air With diminishing release velocity, the flow strain reduces along with quench of the reactive kernel and ignition then occurs at a critical exit velocity The ignition at reducing velocity may ignite the released gas and create a significant combustion or explosion The critical exit velocity of indefinitely delayed ignition lies between 0.3 m/s to 4.3 m/s for vent diameter of 2.03 ~4.32 mm as shown in Figure These velocities are at least two orders of magnitude smaller than the velocity from a pressurized source which in most cases reaches sonic velocity Furthermore, Figure also highlights that the critical velocity is also decreases with decreasing vent size There are factors other than vent size affecting the critical exit velocity Among them, the temperature, moisture and silane combustion powder are the most noticeable factors At higher temperature, the reactive kernel is stronger and thus the critical exit velocity is larger (Liang et al., 2010) Removing the moisture in the air also results in significantly higher critical exit velocity indicating an inhibitory role of moisture on silane ignition (Liang et al., 2010) The inhibitory action of moisture on the silane autoigniton in air is also in consistent with other fuel such as hydrogen and methane Silane combustion produces white to brown powders as shown in Figure These powders are also known to promote ignition but its exact role remains to be studied The presence of a critical exit velocity for prompt ignition of silane release has important implications in the safety of silane operations First of all, almost all current silane uses in the semiconductor, TFT-LCD, and photovoltaic industries are supplied in the form of pressurized cylinders with pressure up 12.5 MPa The high pressure silane is then regulated to 0.8 MPa for the supply tube into the cleanroom and then further regulated down to 0.3~0.45 MPa before feeding into the process chamber Thus, almost all potential leak points in silane utilization have pressure and possible leak velocity higher than the reported critical velocity for prompt ignition In addition, the potential leak points are the cylinder valve, tubing, and tube connections (Huang and Ngai, 2006) The potential release size will be much smaller than 2.03 mm, except for a catastrophic full bore tube rupture Thus, delayed ignition should be considered as the usual case rather than a rare case in most silane operations Gas Safety for TFT-LCD Manufacturing Fig Critical exit velocity for delayed/prompt ignition as a function of vent diameter Fig Typical silane combustion powder 167 168 Features of Liquid Crystal Display Materials and Processes 2.2 Phosphine Phosphine (PH3) is a highly toxic and pyrophoric liquefied compressed gas Phosphine is used primarily as a phosphorus dopant (N-type dopant) in the TFT LCD industry It is typically supplied as a mixture with hydrogen Pure phosphine is a colorless, pyrophoric liquefied gas Although pure samples of phosphine are odorless, the gas often has an odor of garlic or decaying fish due to the presence of substituted phosphine and diphosphine (P2H4) It is a highly toxic gas with a PEL of 300 ppb, an LC50 of 20 ppm for rat at hour exposure Phosphine has a low auto-ignition temperature